Avionic antennas with multiple radiating elements may be used to transmit an omnidirectional pattern or a directional pattern. The accuracy of the pattern may depend upon the accuracy of the amplitudes and phases of the signals driving the antenna. Conventional relatively high power avionic transmitters provide multiple output signals for driving an antenna having a plurality of elements. Such transmitters may include a plurality of similar circuits, each circuit driven from a common source and providing one of the output signals. A typical circuit may include a power amplifier followed by a phase shifter to set a desired output phase and compensate for phase differences introduced by different power amplifiers. The phase shifter necessarily operates at the relatively high power of the output signal. Such phase shifters are expensive and bulky. They consume power and consequently contribute adversely to the thermal characteristics of an enclosed transmitter.
Another type of conventional avionic antenna has fixed phase shift circuits, also known as a beam forming network, integral to the antenna assembly to facilitate transmitting one of a set of directional patterns. To use this antenna to transmit omnidirectionally will require an accurate phase relationship among the signals provided to the ports of such an antenna. These and other issues are addressed by the present invention.